Tamper respondent sensor and enclosure

ABSTRACT

A tamper respondent enclosure including (a) a circuit board; (b) an enclosure surrounding the circuit board; (c) a tamper respondent sensor having (i) a substrate with first and second sides; (ii) a first layer of conductive traces on the first side; (d) wherein the tamper respondent sensor is wrapped around the enclosure with at least one overlap region; and (e) wherein only at the at least one overlap region the tamper respondent sensor has a second layer of conductive traces on the second side. Preferably, the substrate is insulating and made of opaque PET, and the first layer is adjacent the enclosure.

FIELD OF THE INVENTION

This invention relates to tamper respondent enclosures, and inparticular, to a sensor used as a tamper respondent enclosure.

BACKGROUND OF THE INVENTION

Tamper respondent enclosures are used in various applications, includingthe transport of sensitive information and protecting electronicdevices. Typical enclosures are in the form of envelopes and shallowboxes, the walls of which are formed by folding flexible sheetsincorporating tamper detection features. As used herein, sheetsincorporating tamper detection features are known as “sensors”. Thesesheets may also be wrapped around preexisting boxes or enclosures.

Included in such sheets are layers of flexible material and a matrix ofdiagonally extending or zig-zag pattern semi-conductive or conductivelines, also known as conductive traces. The lines or traces are printedon thin insulating film. The matrix of lines forms a continuousconductor which is broken if attempts are made to penetrate the film.The sensor matrix is monitored and when a tamper occurs the electricalstate of the sensor changes. A detection of a change in state caninitiate a signal. This signal can erase information stored within theenclosure, or otherwise protect the information from being discovered.

In known devices, the matrix of semi-conductive or conductive lines ortraces on the insulating film is printed on both sides of the film. Thelines on one side are disposed in the sections of the film opposite fromwhere the lines are disposed on the opposite side. In this manner,complete coverage of the film is obtained, and it is more difficult topenetrate the film without cutting a line, either on one side of thefilm or the other.

Typically, the flexible material is a clear insulating film such as PET.In order to further protect and obfuscate the location of the lines ofthe semi-conductive lines, thereby making it more difficult tocircumvent them in an attempt to break through the film to get to theinformation, known methods include a potting material. This pottingmaterial is typically a dark resin that encapsulates the entire film.The dark potting material provides a mechanical barrier and hides thelocation of the semi-conductive lines.

Although these devices are effective, they are difficult to manufacture.A construction that leads to a more efficient assembly is desired.

SUMMARY OF THE INVENTION

The present invention provides a tamper respondent enclosure including(a) a circuit board; (b) an enclosure surrounding the circuit board; (c)a tamper respondent sensor having (i) a substrate with first and secondsides; (ii) a first layer of conductive traces on the first side; (d)wherein the tamper respondent sensor is wrapped around the enclosurewith at least one overlap region; and (e) wherein only at the at leastone overlap region the tamper respondent sensor has a second layer ofconductive traces on the second side. Preferably, the substrate isinsulating and made of an opaque film such as PET, and the first layeris adjacent the enclosure.

In alternative embodiments, the substrate and enclosure further includean opening for communication between the circuit board and an externaldevice. In exemplary embodiments, the external device is a computermother board, a connector, and a cable. The circuit board in analternative embodiment includes a wireless transmitter.

In preferred embodiments, the tamper respondent sensor is shaped toallow only two layers at the at least one overlap region, and the secondside of said substrate has no exposed conductive traces. Also in apreferred embodiment, the substrate further includes an adhesivedisposed over the first layer of conductive traces. The adhesive ispreferably a pressure sensitive adhesive (PSA).

In another aspect, the present invention provides a tamper respondentsensor including (a) a substrate having a first side and a second side,the substrate adapted to be folded to produce an overlapping portion ofthe first side with an overlapping portion of the second side; (b) afirst layer of conductive traces on the first side; (c) a second layerof conductive traces only at the overlapping portion of the second side,(d) the second side having a region free of conductive traces, (e) thesecond layer of conductive traces being electrically connected to thefirst layer of conductive traces. Preferably, the traces are in anunpredictable pattern. The tamper respondent sensor preferably furtherincludes an input/output (I/O) lead.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side sectional view of a prior art sensor.

FIG. 2A is a schematic side sectional view of a sensor according to anexemplary embodiment of the present invention.

FIG. 2B is a schematic side sectional view of a sensor according to anexemplary embodiment of the present invention.

FIG. 3A is a schematic showing an exemplary sensor according to thepresent invention in an unwrapped and a wrapped state.

FIG. 3B is a schematic showing an exemplary sensor of the presentinvention in an unwrapped and a wrapped state.

FIG. 4A is a bottom view of an exemplary sensor according to the presentinvention.

FIG. 4B is a top view of an exemplary sensor according to the presentinvention.

FIG. 5 is a schematic side sectional view of a sensor according to anexemplary embodiment of the present invention.

FIG. 6 is a top view of an exemplary sensor according to the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a schematic diagram of a prior art tamper respondentenclosure. Circuit board 100 has components 101 disposed thereon.Components 101 contain the sensitive information that is desired to beprotected. A box or enclosure 102 surrounds circuit board 100 andcomponents 101. Enclosure 102 has a sensor 103 disposed around it.Sensor 103 comprises a clear PET substrate 104. On both sides of PETsubstrate 104 are disposed printed traces 105. This is a matrix ofconductive lines on each side. The lines are disposed in offsettingrelation from one side to the other to ensure complete coverage of PETsubstrate 104. The inside of PET substrate 104 also has a layer ofadhesive 106 disposed over the printed trace 105 on that surface.Adhesive layer 106 is a pressure sensitive adhesive (PSA). In this priorart device, the entire sensor is then encapsulated in an opaqueencapsulant or potting material 107. Potting material 107 helpsobfuscate printed traces 105. An outer shell 108 surrounds the device. Acable 109 is used to connect components 101 with exterior components110. Although the top section of sensor 103 is shown to be open, this isfor illustration purposes only. In use, the overlapping ends of sensor103 are secured to one another by adhesive layer 106.

Although this device is effective, it is difficult to manufacture. Itincludes the deposition of printed traces on two sides of the PETsubstrate and it also includes the potting layer 107.

FIG. 2A is a schematic representation of an exemplary embodiment of thepresent invention. As shown in FIG. 2, a circuit board 20 has components21 disposed thereon. Components 21 contain sensitive information to beprotected. In alternative embodiments, circuit board 20 can includewireless transmitters as components 21. Circuit board 20 and components21 are enclosed by a box or enclosure 22. Enclosure 22 may be any shape.A rectangular shape is shown in this embodiment, but it may also betrapezoidal, wedge-shaped, or any other shape. Enclosure 22 isencapsulated by tamper respondent sensor 10. In alternative embodiments,tamper respondent sensor 10 may be wrapped around a circuit boardwithout a preexisting box or enclosure, in which case a filler may beused to form a surface over the circuit board to which tamper respondentsensor 10 adheres.

Tamper respondent sensor 10 includes a substrate 11. Preferably,substrate 11 an insulating material such as PET. According to thisinvention, substrate 11 is opaque. By using an opaque PET for substrate11, it is not necessary to subsequently pot the material in order toobfuscate the printed traces.

Substrate 11 has a first side 12 and second side 13. First side 12 isthe inside of the substrate as illustrated in FIG. 2A. Disposed on thisfirst side 12 is a first layer of conductive traces 14. Preferably, theconductive traces are made of a conductive, non-metallic ink, such ascarbon-loaded polymer resin as taught, for example, in U.S. Pat. No.5,539,379. Other materials known in the art may be used for the traces.

Substrate 11 is adapted to be folded to produce an overlapping portionof first side 12 with an overlapping portion of second side 13. Onsecond side 13, which is the outer side of substrate 11 in theillustrated embodiment, a second layer of conductive traces 15 isdisposed. Second layer of conductive traces 15 is present, however, onlyat the overlapping portion of second side 13. That is, second layer ofconductive traces 15 is only disposed on that portion of second side 13where there is an overlap with first side 12. The remainder of secondside 13 is a region free of conductive traces. Thus, there are noexposed traces on second side 13.

The traces on second side 13 are electrically connected to the traces onfirst side 12, for example by a via. Preferably, the vias are located atthe overlapping portion. A monitor (not shown) detects the circuitcompleted by first layer of conductive traces 14 and second layer ofconductive traces 15 and monitors the electrical state. If thiselectrical state changes, indicating that the circuit has been broken,for example by cutting one of the traces, the monitor can trigger aresponse such as erasing information stored in components 21.

As shown in FIG. 2A, the overlap region is open for purposes ofillustration. In use, the overlap is mated such that second layer ofconductive traces 15 is adhered to first layer of conductive traces 14by an adhesive layer 30. Adhesive layer 30 is preferably a tackifier,such as a PSA. Adhesive layer 30 is disposed on first side 12 ofsubstrate 11 on the first layer of conductive traces 14. In this manner,once mated, if someone tries to tamper with sensor 10, by liftingsubstrate 11 at the overlap, adhesive layer 30 will sever either firstlayer of conductive traces 14 or second layer of conductive traces 15,thereby causing an interruption in the signal and triggering erasure orother protection of information stored in components 21 as describedabove. There may be one or a plurality of overlap regions of sensor 10in final use. Preferably there are only two layers of substrate 11 ateach overlap region.

As shown in FIG. 2B, a cable 71 is used to connect components inside thedevice to components outside the device.

FIG. 3A and FIG. 3B show alternative embodiments of the presentinvention. The embodiments represents a sensor 10 for use in wrapping anenclosure of a rectangular shape (FIG. 3A) and a wedge shape (FIG. 3B).The portion of FIGS. 3A and 3B labeled “unwrapped” shows sensor 10 inits intermediate form. Once an enclosure is placed on sensor 10, sensor10 is then wrapped around the enclosure to completely encapsulate it, asillustrated in the portion of the figures labeled “wrapped.”

FIG. 4A is a bottom view of an exemplary sensor 10 according to thepresent invention. FIG. 4B is a top view of sensor 10. As shown in FIGS.4A and 4B, sensor 10 includes substrate 11. In the present invention,substrate 11 is an opaque film such as PET. First side 12 of substrate11 has first layer of conductive traces 14 disposed thereon.

In a preferred embodiment of the present invention, traces 14 aredisposed in an unpredictable pattern on substrate 11. This is incontrast to diagonal (zig-zag), straight, or sinusoidal wave trace linesknown in the art. Because these known patterns repeat at regularintervals, it potentially makes the sensor vulnerable to a jumper attackwherein the attacker can locate two points of the same trace and bypassthe trace with a conductive jumper. Potentially, the attacker can thenpenetrate the sensor without triggering a change in electrical state. Byusing an unpredictable pattern, it is more difficult to break intosensor 10 because it is difficult to follow a single conductive traceand bypass it with a jumper. In order to make the unpredictable pattern,the trace herein is manually drawn using computer-aided softwarepackages such as PCB-PADS®, from Mentor Graphics, a printed circuitboard layout software program.

As shown in FIG. 4A, a second layer of conductive traces 15 is disposedon the portions of second side 13 of substrate 11 that will overlap withfirst side 12 as described above. The remainder of second side 13 is aregion free of conductive traces. Thus, there are no exposed traces onsecond side 13 once it is wrapped around an enclosure.

Also shown in FIGS. 4A and 4B is an opening 20 in sensor 10 which ispreferably included in sensor 10 to allow mating of a circuit board 20with another device external to sensor 10. The external device can be acomputer mother board, a connector, or a cable, for example. FIG. 5illustrates an exemplary embodiment wherein opening 20 allows mating ofcomponent 21 to a connector 80. Also shown in FIGS. 4A and 4B is an I/Olead 40 extending from substrate 11. FIG. 6 is a top view of exemplarysensor 10 without opening 20. This sensor 10 of FIG. 6 would beconnected using a cable through the overlap zone as shown in FIG. 2B.

The present invention provides distinctive advantages over the knownart. Specifically, employing an unpredictable pattern for the tracesmakes it more difficult to defeat the device. In addition, using anopaque PET for substrate 11 obviates the need to pot the sensor. Thiseliminates a processing step, making production more efficient and costeffective. It also provides natural obfuscation for the conductivetraces which may render the use of a second layer of conductive tracesover the entire second side 13 of substrate 11 unnecessary. This alsoeliminates processing steps increasing efficiency and reducing costs. Byselectively putting the second layer of conductive traces 15 only atportions of the second side 13 where substrate 11 overlaps, an effectivetamper respondent enclosure is produced.

In the illustrated embodiments, relatively small overlapping portionsare depicted. In alternative embodiments, larger overlapping portionsare used, for example covering an entire side of box 22 or furthermoreall sides of a box.

While particular embodiments of the present invention have beenillustrated and described herein, the present invention should not belimited to such illustrations and descriptions. It should be apparentthat changes and modifications may be incorporated and embodied as partof the present invention within the scope of the following claims.

1. An article comprising: (a) a circuit board; (b) a tamper respondent sensor having (i) a substrate with first and second sides; (ii) a first layer of conductive traces on said first side; (c) wherein said tamper respondent sensor has a first unwrapped form having an irregular, non-rectangular shape, and a second wrapped form, wrapped around said circuit board with at least one overlap region; (d) wherein only at said at least one overlap region said tamper respondent sensor has a second layer of conductive traces on said second side.
 2. An article as defined in claim 1, wherein said substrate is an opaque insulating film.
 3. An article as defined in claim 1, wherein said substrate is PET.
 4. An article as defined in claim 1, wherein said first layer is adjacent the circuit board.
 5. An article as defined in claim 1, wherein said substrate further comprises an opening for communication between said circuit board and an external device.
 6. An article as defined in claim 5, wherein said external device is a printed circuit board.
 7. An article as defined in claim 5, further comprising a connector attached to said circuit board and disposed in said opening.
 8. An article as defined in claim 5, further comprising a cable attached to said circuit board and disposed in said opening.
 9. An article as defined in claim 1, wherein said circuit board further comprises a wireless transmitter.
 10. An article as defined in claim 1, wherein said tamper respondent sensor is shaped such that there are only two layers of substrate at said at least one overlap region.
 11. A tamper respondent sensor as defined in claim 1, wherein said second side of said substrate has no exposed conductive traces.
 12. A tamper respondent sensor as defined in claim 1, wherein said substrate further comprises an adhesive.
 13. A tamper respondent sensor as defined in claim 12, wherein said adhesive is disposed over either said first layer or said second layer of conductive traces
 14. 14. A tamper respondent sensor as defined in claim 12, wherein said adhesive is a PSA.
 15. A tamper respondent sensor comprising: (a) a substrate having a first side and a second side, said substrate having a first unwrapped form having an irregular, non-rectangular shape, and a second wrapped form, folded to produce an overlapping portion of said first side with an overlapping portion of said second side; (b) a first layer of conductive traces on said first side; (c) a second layer of conductive traces only at said overlapping portion of said second side, (d) said second side having a region free of conductive traces, (e) said second layer of conductive traces electrically connected to said first layer of conductive traces.
 16. A tamper respondent sensor as defined in claim 15, wherein said substrate is opaque.
 17. A tamper respondent sensor as defined in claim 15, wherein said substrate is insulating.
 18. A tamper respondent sensor as defined in claim 15, wherein said substrate is PET.
 19. A tamper respondent sensor as defined in claim 15, wherein said substrate further comprises an adhesive.
 20. A tamper respondent sensor as defined in claim 19, wherein said adhesive is disposed over said first layer of conductive traces.
 21. A tamper respondent sensor as defined in claim 19, wherein said adhesive is a PSA.
 22. A tamper respondent sensor as defined in claim 15, further comprising an opening.
 23. A tamper respondent sensor as defined in claim 15, wherein said traces are in an unpredictable pattern.
 24. A tamper respondent sensor as defined in claim 15 further comprising an I/O lead.
 25. A tamper respondent sensor as defined in claim 15 further comprising at least one via through said substrate at said overlapping portion connecting said first layer of conductive traces to said second layer of conductive traces. 